1. Field of the Invention
The present invention relates to an apparatus for detecting an arc fault, and more particularly, to an apparatus for detecting an arc fault, which first prevents a malfunction caused by a conventional current detecting method by detecting a source voltage applied onto a conductive wire to determine whether there is an arc fault, prevents a malfunction with respect to a pseudo arc signal by dividing a current detecting route into two according to the magnitude of a load current occurring onto the conductive wire to determine whether there is the arc fault by voltage detection, and lessens the danger of a fire by reducing a circuit break time according to the magnitude of the load current.
2. Background of the Invention
Arc faults, such as a series arc fault, a parallel arc fault and a ground arc fault, are generated via an electric wiring due to physical, electric faults caused by an aged wiring, breakdown of a wiring, insulation failures, overcurrents, etc. Since the arc faults are the cause of a fire, it is mandatory in the U.S. to use an arc fault circuit interrupter (AFCI) for breaking a circuit of electric equipment upon an occurrence of an arc fault.
In detecting an arc fault, it is necessary to discriminate between an arc signal, and a pseudo arc signal, that is, a signal generated when electric equipment is activated or when a dimmer is operated.
A conventional arc fault detector, in some cases, breaks a circuit by regarding an electric equipment starting signal or a dimmer signal as an arc fault signal.
An improved arc fault detecting apparatus for preventing such a malfunction is disclosed in Korean patent application No. 10-2002-71166.
FIG. 1 illustrates the apparatus for detecting an arc fault, disclosed in the above patent application.
Referring to FIG. 1, the apparatus for detecting an arc fault comprises a current detector 500 for detecting the amount of change in current flowing onto a conductive wire between a power source 520 and a load 522 and generating a signal proportional to the amount of change, a signal transformer 502 for passing a signal having a high frequency component out of the signal output from the current detector 500 and limiting a level of the signal so as not to exceed a predetermined signal level, a first level limit amplifier 504 for limitedly amplifying the signal output from the signal transformer 502, a high pass filter 526 for passing a signal having a high frequency component out of the signal output from first level limit amplifier 504, a second level limit amplifier 506 for amplifying the signal output from the high pass filter 526, a second arc determination unit 524 for determining whether an arc is detected by integrating the output signal of the second level limit amplifier 506 for a predetermined time, a signal level detector 508 for determining whether the input signal exceeds a predetermined first reference voltage and generating a detection signal, a pulse generator 510 for transforming the detection signal output from the signal level detector 508 into a pulse signal having a normalized form, a first arc determination unit 512 for counting the pulse signal output from the pulse generator 510 for a predetermined time, determining whether an arc occurs, and generating an arc detection signal, and a circuit breaker 514 breaking the conductive wire when the arc detection signal is generated.
In operation, the current detector 500 detects the amount of change of current flowing onto the conductive wire between the power source 520 and the load 522 and generates a signal proportional to the amount of change.
The signal transformer 502 receiving the output signal of the current detector 500 passes a signal having a high frequency component and limits a level of the signal so as not to exceed a predetermined signal level. The output signal of the signal transformer 502 is input to the first level limit amplifier 504. Accordingly, the signal transformer 502 serves as a determiner for detecting a high frequency signal, i.e., an arc signal.
The first level limit amplifier 504 amplifies the signals output from the signal transformer 502 by limiting the amplification level in order to detect the arc signal having a lower amplitude than an amplitude of a main signal.
A noise component of the output signal of the first level limit amplifier 504 is eliminated through the high pass filter 526 passing only the signal having a high frequency component, and the output signal of the high pass filter 526 is input to the second level limit amplifier 506.
The second level limit amplifier 506 amplifies the signal output from the high pass filter 526, and the amplified signal is input to the second arc determination unit 524.
The second arc determination unit 524 determines whether an arc is detected by integrating the output signal of the second level limit amplifier 506 for a predetermined time in order to judge an arc which is instantaneously generated like a parallel arc.
The signal level detector 508 determines whether the input signal exceeds a predetermined first reference voltage and generates a detection signal.
The detection signal output from the signal level detector 508 is applied to the pulse generator 510. The pulse generator 510 transforms the detection signal output from the signal level detector 508 into a pulse signal having a normalized form.
The first arc determination unit 512 counts the pulse signal output from the pulse generator 510 for a predetermined time, determines whether an arc occurs, and generates an arc detection signal. That is, the first arc determination unit 512 determines whether the pulse signal output from the pulse generator 510 is an arc signal, a dimmer signal, or an activation signal by counting the number of pulses. If the pulse signal is judged to be an arc signal, the first arc determination unit 512 outputs a break signal to the circuit breaker 514 so as to break the circuit.
The above-described apparatus determines whether an arc fault occurs or not by detecting current flowing onto the conductive wire between the source and the load.
In order to detect the current, a current sensor called a current transformer (CT) using a ring core is employed. The detecting range or characteristic of current flowing onto the conductive wire differs according to the material or operational properties of the current transformer.
The output signal of the current transformer is determined in proportion to the number of windings of a coil wound around a core with respect to an input signal. However, in order to obtain the accurate output according to the magnitude of the input current, the huge number of windings of the coil is needed and as a result the size of the current transformer and core is increased.
For example, in detecting current flowing onto a phase (hot) conductive wire by using the current transformer, if the current of 10 amperes flows onto the conductive wire, the output signal of 5 voltages is detected, and if the current of 5 amperes flows, the output signal of 10 voltages is detected.
Although this current detecting method can easily detect the arc signal, a signal similar to the arc signal is also detected and thus there is a strong probability of a malfunction.
Furthermore, since the conventional arc fault detecting apparatus detects the arc signal by a single route without discriminating between a low current and a high current, many problems occur in setting a frequency band, or a circuit break time from an occurrence of the arc signal to the break of the circuit.